Help with domain and server/client url

I have the domain coolthing.nl now when i add this custom domain using fly.io what does the server and client url change to?

Right now it is:
https://coolthing-server.fly.dev
and
https://coolthing-client.fly.dev

But for my other programs and apps that interact with the server i need to know what the server url becomes when changing the domain to coolthing.com